Liquid-vapor phase differential fire and overheat detector and control



March 1, 1960 J, 0 s 2,927,309

- LIQUID-VAPOR PHASE DIFFERENTIAL FIRE AND Filed NOV. 2, 1953 OVERHEAT DETECTOR AND CONTROL 2 Sheets-Sheet 1 March 1, 1960 E. J. POITRAS 2,927,309

LIQUID-VAPOR PHASE DIFFERENTIAL FIRE AND OVERHEAT DETECTOR AND CONTROL Filed Nov. 2, 1953v 2 Sheets-Sheet 2 o i g g L-d, "'5 El m J o g BP2 '2 1 t2 5 E M g is RANGE l-IJ l- DISTANCE ALONG SENSING ELEMENT ZONE van lwezaiow: EmwdJPaia-m, 11 Fm? '9 512302 221295 United States Patent LIQUID-VAPOR PHASE DIFFERENTIAL FIRE AND OVERHEAT DETECTOR AND CONTROL Edward J. Poitras, Holliston, Mass. Application November 2, 1953, Serial No. 389,603

14 Claims. (Cl. 340-227 This invention relates generally to fire and overheat detection, and more particularly to improvements in apparatus affording such protection by differential measurement and without averaging effect. It provides further a detector etfecting continuous warning and control in a spatially extensive area, and like that shown and described in my co-pending application, Serial Number 293,691, filed June 14, 1952, now Patent No. 2,658,190 of November 7, 1953, of which this application is a continuation inpart.

My present invention aims generally to provide a fire and overheat detector of the class described which embodies both single and twin tube sensing elements and which is characterized by substantially greater sensitivity, and by a more prompt and more accurate response to any temperature rise from the safe, normal, or ambient range to an unsafe, detectable or fire and overheat level. In the form herein shown and described my improved detector is distinguished further by differential volumes having a solid liquid fill differentiated as to predictable temperature of liquid-vapor change, and normally differentiated also as to coefiicient of volumetric expansion. The invention will be understood also to be specially adapted toapplications such as air craft power plants where the ambient ranges are wide, temperature gradients are steep, expected length of overheat is variable, and control temperatures are high.

The apparatus of this invention parallels that disclosed and described in my above-mentioned application in the elimination of the so-called averaging effect, by which previous detector systems of the class herein concerned have been characterized. By averaging eifect is meant the inability to distinguish a safe temperature rise in the ambient range and over a relatively long length of the continuous sensing element from an unsafe temperature rise to a fire and overheat level and over a relatively short length of the detector. Thus in the conventional systems the alarm sensitivity varies with and is limited by the ambient range and also by detector length and expected length of overheat.

Referring still to the prior continuous detectors, the same are characterized generally by a single sensing element or channel and communicating distensible chamber or bellows charged with a fluid, generally air. While detecting, as by a volumetric increase measurable at said bellows, a temperature rise to the level to be detected or controlled over a relatively short length of their sensing element, they will be seen to respond by similar volumetric increase to an ambient temperature change over a substantially greater length of said element. The sensitivity of a conventional detector is thus a function of the ambient range, and limited at the lower end of such range to the length of the sensing element equal to the change in length of its fluid column responsive to the largest expectable change in ambient temperature.

The improved, sensitive, nomaveraging detector of this and my co-pending application above mentioned may generally be described as providing differential or compared 2,927,309 Patented Mar. 1, 1960 Ice volumes either in parallel sensing channels or variously in a single sensing channel and parallel compensator unit. These contrasted volumes are arranged and conditioned in accordance with the invention for detecting by parallel, non-differentiating, and therefore non-signalling response the safe, normal, or ambient temperature changes. One embodiment disclosed in my co-pending application provides, for example, identical tubes and bellows, the tubes generally parallel and closely spaced so that corresponding locations on them have identical temperatures under all conditions. These identical tubes and bellows are solid-filled with liquids of like coefiicients of volumetric expansion, but differentiated as to boiling points. Thus the differentiating or detected and signalled thermal changes are those only which reflect a temperature rise to the boiling point of the lower boiling liquid. My improved detector, then, is independent of thermal changes in the ambient range; its signalling is unrelated to ambient range width or sensing element length; and its sensitivity is limited only by the manufacturing tolerances governing the minimum differential deflection necessary to an intelligible signal. It follows that the detector of this invention, detecting and signaling only those thermal changes occurring at control temperatures as defined by the boiling point of a lower boiling liquid, is uniquely free from the ill effects of variations in rate of change through the ambient range. As will more fully appear hereafter," it is uniquely adapted also to fire and overheat situations wherein steep temperature gradients occur.

Referring now more particularly to the detector as novelly shown and described herein there is provided generally a differential measurement arising in the use of liquids differentiated as'to coefficients of volumetric expansion. These liquids define parallel sensing element columns in one embodiment, and a single column and parallel-associated compensating unit in another.

The invention will be better understood from a consideration of the following specifications taken in conjunction with accompanying drawing in which:

Figs. 1 to 5 show schematically several operational conditions of the paired or twin tube embodiment where- Fig. 1 represents the normal or non-emergency status with the ambient temperature near or at the low level of the range;

Fig. 2 indicates an approach to the high level of the ambient range but without overheat or fire;

Fig. 3 representsan emergency or alarm condition such as fire or overheat at some location on the sensing element; 7

Fig. 4 shows an emergencyor alarm condition similar to that of Fig. 3, but wherein the fire or overheat condition is over a longer length of the sensing element; and

Fig. 5 illustrates the total vaporization of the liquid from both sensing element channels under extreme high temperatures.

Fig. 6 is a graphic representation of the liquid-vapor phase condition along the sensing element as a function of surrounding temperatures.

Fig. 7 shows schematically the modification employing one or morecompensator units in place of the second tube of the twin tube system; and

Fig. 8 is a sectional view of a variant form of th modification bf Fig. 7.-

Ondembodim'e'nfof my improved differential, nonaveraging fire andoverheat detector is represented in Figs. 1 to 5 inclusive, as comprising generally a pair of 'rigid'elongate sensing elements, channels or tubes 1, 2 extending continuously about or through the area to be protected and controlled, "andin such close thermal or physical associationas to be identically responsive to temperature conditions obtaining therein. The tubes 1, 2 are dead-ended as shown and are coupled at their open ends to variable volume chambers or bellows 3, 4.

In accordance with the invention, the differential or compared detector volumes are made unequal, herein by difierentiation of the channel bores or bellows diameters. Thus in the illustrated embodiment, the equal length detector tubes 1, 2 are differentiated as to volume per unit length, the tube 1 being given a smaller bore.

Further in accordance with the invention the liquids selected for filling the tubes 1, 2 and bellows 3, 4 are predeterminedly differentiated as to coefficients of expansion, such as would efiect differential change or movement in the bellows 3, 4 for like temperature changes in detector tubes of like volume. It will be readily apparent that for the desired non-differentiating response to ambient temperature changes, the mentioned difierentiation of the detector volumes is calculated or defined as that which will compensate exactly for this differentiation of expansion coefficients. In the illustrated embodiment, the bellows 3, 4 are of like diameter, and the bore of channel 2 has been indicated as the larger, so that the liquid with higher volumetric expansion coefficient is placed in channel 1.

The channels 1, 2 and communicating bellows 3, 4 are completely or solid-filled with liquids selected and conditioned for boiling levels or points at temperatures obtaining under and reflecting the emergency or fire and overheat conditions to be controlled or detected. Further, the channel and bellows filling liquid volumes are differentiated as to boiling point, one from the other, such that the liquid of one channel, for example channel 1, has a higher boiling point than that of the liquid of the other channel, herein channel 2.

Various means may be provided for sensing and signalling the differential movement of the bellows 3, 4 subject to liquid-vapor change and as responsive to emergency or alarm conditions in the region of the tubes 1, 2. Such means are shown as an electrical circuit and contact pair 5 arranged for opening and closing movement by and with the like relative movement of the bellows, and incorporating means such as the lamp 6 for visual or other proximate or remote indication.

With the embodiment of my improved continuous detector just described and herin illustrated in Figs. 1 through 5 inclusive, ambient changes and thermal conditions along all or at any part of the sensing elements 1, 2 will be reflected by absolute but not relative or differential movement of the bellows 3, 4 and contacts 5.

Thus, for a given temperature rise in the ambient range the relatively greater expansion in the relatively larger diametered tube or channel 2 having the larger volume per unit length is compensated by the higher coeflicient of expansion of the liquid in the smaller diametered channel 1. Accordingly and at some point at the lower end of the ambient range, the bellows 3, 4 will occupy the parallel and relatively collapsed positions of Fig. 1, and the contacts 5 will occupy the normal separated or disengaged positions there shown. Upon a temperature rise over a significant portion of the tubes 1, 2 to the upper limit of the ambient range, the bellows 3, 4 will expand or distend to the relatively elevated positions of Fig. 2 in identical mannerand without relative movement of the contacts 5. Thus to any and all ambient temperature changes over any and all significant portions of their length, the sensing element volumes respond by an expansion reflected at the bellows 3, 4 by parallel, non-differentiating movement, or movement in the same direction and to the same extent. 7

Referring now to th'egraphof Fig. 6; wherein the vertical axis represents temperature of the sensing element and the horizontal axis represents the distance along the sensing element, the curves 1, t t indicate the lower and upper limits and a random intermediate point respectively in the ambient'range, and the curves BP; and BP:

are seen as the relative higher and lower boiling points of the channel 1 and 2 liquids respectively. It will be readily appreciated that the curve for the ambient range bellows deflection as just described is without differential aspect, reflecting no liquid-vapor change, and being limited below the ambient range cure t and also being identical for both tubes.

Should, however, the temperature of the area to be protected rise above the safe, normal, ambient range to an unsafe, detectable or fire and overheat level, and more particularly to a level above the boiling point of the lower boiling liquid, herein that filling the channel and bellows system 2, 4, such rise will be reflected at the detector by differential movement of the bellows 3, 4 causing signalling and engagement of the contacts 5. in other words, heating of the area to be controlled along a minimum length of the tubes 1, 2 and above the boiling point of the lower boiling liquid effects a vaporization of that liquid over that length, compelling the ejection of liquid from the lower boiling channel and the resultant corresponding differential distention of the associated bellows.

Such differential signalling detector response is indicated in Figs. 3 and 4 of the drawing, wherein some part of the sensing element has become heated above the ambient level, where the ambient temperature is relatively low in Fig. 3 and higher in Fig. 4, and to a temperature at least as high as the boiling point of the lower boiling liquid of channel 2 and bellows 4, the attendant liquidvapor change forcing distention of the bellows 4 differential as to the bellows 3, since nowwhere along the sensing element has the temperature reached the boiling temperature of the channel 1 liquid. This condition is represented by the solid line curve at the left, Fig. 6, wherein the distance d indicates the length of the sensing element over which the lower boiling liquid of channel 2 has been vaporized, and similarly the length of the liquid column displaced from channel 2 by the indicated change to vapor phase.

Fig. 3 therefore represents a localized heating to a temperature in the differential range between the two boiling points of a sufficient length of the sensing element to distend the bellows 4 differentially beyond bellows 3, so as to close the contacts 5 and effect an alarm signal, as by lighting the lamp 6.

As an important feature of the invention there is provided at the bellows 3, 4 a built-in or inherently accentuated indication. Such enhanced sensitivity of my proved detector devolves from the earlier described differentiation of the channels 1, 2 wherein they provide relatively smaller or larger volumes per unit length, and from the fact that compensation of the expansion in such volumes is effected only in the ambient range. Thus upon overheating of or more particularly a liquid-vapor change in and over any length of the lower boiling liquid column 2 of the sensing element there is had a relatively greater relative or differential movement of the bellows 3, 4 than with tubes and liquids of like bore and like expansion coefficient such as considered in my co-pending application, and by reason of the relatively greater volumetric discharge per unit length of vapor change in the said larger diametered, lower boiling channel 2. Thus in the present embodiment, my improved detector is seen to have substantially increased sensitivity, and to be limited as to operational sensitivity only by internal friction and by manufacturing tolerances. It may be noted that the more sensitive response and accentuated indication just described assumes significant proportions particularly under those operating conditions wherein steep temperature gradients occur, and under which the desired promptness and accuracy of detection may be difficult to achieve under existing manufacturing tolerances.

Another important advantage of the present embodiment is illustrated in Fig. 5, wherein the detector is represented as in the relatively unusual condition of total vaporization of the liquids from the channels 1, 2. It will be observed that in, view of the inequality of the detector volumes, the desired differential movement of the bellows 3, 4 and operation of the alarm circuit 5, 6 occurs as well under conditions of longest or greatest expectable overheat.

The condition of heating of at least a minimum length of the sensing element to a level above the boiling point of the higher boiling liquid of channel 1 is represented by the dotted line curve at the right in Fig. 6, wherein the differential displacement of the bellows is the sum of d d The accentuated response and indication earlier described for my present embodiment will be seen as a greater differential distance d d of bellows motion than with the embodiment of my co-pending application.

Further in accordance with the invention, there is provided a single tube sensing element and associated compensating unit also'embodying the liquids of different expansion coefiicients and herein illustrated by the modifications of Figs. 7 and 8. Referring now more particularly to Fig. 7, there is shown a rigid, continuous, elongate sensing element comprising a single channel or tube 10 and having extent corresponding to the area to be controlled or protected, and serially divided as the area or otherwise into operative zones A, B, N, providing unit detector volumes V V V The tube 10 is closed at one end and joined at the other to a variable volume chamber or bellows 11 in operative association with the fixed and movable alarm contact pair 12 as shown. A series of compensator units 20 are seen generally as mounted in parallel association with the sensing element 10. Said elements 20 are shown more particularly to comprise variable volume chambers or bellows 21 providing compensator volumes V Vzb, V in parallel communication with the respective detector volumes V V and V The compensator units 20 comprise further the variable volume chambers orbellows 22 mechanically linked to the bellows 21 providing separated or non-communicating control volumes an, V V In the embodiment of Fig. 7 the control bellows 22 are seen more particularly as concentric and continuous at their ends with their respective compensating bellows 21.

The several volumes defined by the tube 10, first bellows 11, and bellows 21, 22 are completely or solid-filled with liquids selected as before for boiling points in the fire and overheat range. Further, the variable volumes 21, 22 are so proportioned that expansion of a liquid trapped in the control volumes 22 will under conditions of ambient temperature change distend the bellows 22 and with it the bellows 21 by an amount just sufficient to offset or take up the expansion in the corresponding detector volume, as well as that occurring in the bellows 21. Thus during ambient temperature changes no fluid is ejected at the end of the tube 10 to distend the bellows 11; therefore no motion occurs at the alarm unit 12.

It will be appreciated that the volumes V V V may be charged or filled with the same or different liquids. If the volumes V V contain a fluid of expansion coefficient K and the trapped volumes V carry a fluid of expansion coefficient K the relationship for static compensation will be:

where A is the area of a control bellows 22 and A is the area of a compensator bellows 21. Alternatively the same liquid may be used in the detector compensator volumes V V as in the trapped or control volumes V As the boiling point of the system V V is determined by the relationship of the force F0 of the spring 13 to the area A0 of the bellows 11 and that of the system V depends upon the relationship of the force FA of the spring 23 to the total area of the volumes V V in the instance of a common fluid in volumes V V V and for the necessary differentiation of the boiling points in the systems, the force-area relationships will be:

a F0 A,+A, Ao

It should be noted that in the embodiment of Fig. 7 the control volumes are substantially surrounded and insulated by the compensator volumes, resulting in a de sired anticipation effect, or expansion in the compensator volumes during a temperature rise slightly ahead of that occurring in the control volumes V This effect could be controlled or accentuated as desired by providing suitable thermal insulation around the said control volumes V The numerous volume expansion and proportion relationships possible in a system such as just described may be met in many ways. For example, the bellows may be provided and proportioned to suit exactly the given requirements. 'Variously, a limited number of standard bellows may be provided and final adjustment obtained by inserting a bit of wire inside the tube 10 or by otherwise taking up some of the volume in the compensator bellows 21.

In the modification illustrated in Fig. 8, a separate bellows and linkage arrangement is employed. More particularly, the compensator and control bellows, V V are supported in parallel from a common base 30 and interrelated as regards distention by a lever arm 31, the latter pivoting at a fulcrum 31a and pressing against bellows V as at 32, by virtue of spring 33. It will be seen that in this modification the action of the control bellows V may be variously multiplied to suit any given volume V by adjustment of the fulcrum 31a along the base 30, and that suitable indicia 30a may be provided, calibrated in feet of tubing V to facilitate the necessary adjustment.

From the foregoing it will be appreciated that my present invention affords improvements in a continuous fire and overheat detector wherein a more prompt, accurate, and accentuated response is had, particularly in extended overheat and steep temperature gradient situations. This invention has been shown further to be characterized by twin tube or single tube and compensator differential liquid volumes charged with liquids differentiated as to coefficients of volumetric expansion. It will be understood further that the apparatus of the invention may be employed as well for temperature control.

It will be understood that my invention, either as to means or method, is not limited to the exemplary embodiments herein illustrated or described, and I set forth its scope in my following claims.

I claim:

1. A non-averaging fire and overheat detector and temperature control comprising parallel sensing elements each including a terminal expansible chamber, said elements differentiated in volume per unit length, liquid volumes filling said elements, said volumes differentiated as to boiling point and expansion coefiicient and being correlated with the corresponding element volume to effect differential distention of said chambers only at a predetermined overheat temperature at any length of said channels, and an alarmand control circuit associated with said chambers and operative upon their differential distention.

2. In a fire and overheat detector, similar parallel detector tubes communicating with dissimilar bellows, fluid volumes filling said tubes and bellows and difierentiated as to boiling point and expansion coefficient and correlated with respect to ambient temperature effects, so as to order differential movement of said bellows only upon heating of said tubes to predetermined overheat and fire temperatures at said tubes, and means associated with said bellows for sensing and signalling such movement.

3. The combination in a fire and overheat detector of a sensing element comprising generally parallel, closely spaced tubes of equal length and unequal volume, said tubes closed at one end and communicating at the other end with deformable bellows of equal length and volume, filling quantities of liquid in said tubes and bellows, said liquid quantities having different boiling points and expansion coefiicients' in correlation with the different tube volumes so as to order differential distention of said bellows only upon overheating of said tubes, and means associated with said bellows for signalling said differential distention.

4. A fire and overheat detector according to claim 3 wherein the liquid quantity in a larger tube has a lower boiling point and a lower expansion eoefiicient.

5. A fire and overheat detector comprising a sensing channel and a deformable signal-effecting unit, said chan nel and unit coupled and liquid filled, and at least one compensating unit along and associated with a corresponding zone of said channel and comprising a variable volume element containing fluid of different boiling point and expansion coefficient from that of said sensing chan nel and being subject to the thermal status of the latter for compensating for normal expansion in said sensing channel so that only liquid-vapor phase change in said channel produces signal-efiecting deformation of said deformable unit.

6. A fire and overheat detector according to claim 5, wherein the liquid filling said sensing channel and compensating unit is selected or conditioned to boil at overheat temperatures.

7. A fire and overheat detector comprising coupled, fluid-filled detector tube and a first bellows; one or more compensator units spaced along said detector tube and comprising each a communicating compensator bellows for compensating ambient expansion in said detector tube due to temperature change ambient thereto at the locational zone of the respective compensator bellows and associated automatic means controlling the volume of said compensator bellows as appropriate for said ambient ex- A pansion; and contact and circuit means operable for signalling distention of said first-mentioned bellows responsive to overheat temperatures at said detector tube.

8. A fire and overheat detector comprising a sensing element including a channel and end-connected bellows, one or more parallel mounted compensating units on said element and comprising each a coupled variable volume chamber and a separate and sealed variable volume chamber arranged for parallel distention with the coupled chamber, filling quantities of liquid in said channel, chambers and bellows, the liquid trapped in said separate chambers selected and conditioned to regulate the volumes of the channel-coupled chamber of the corresponding unit thereby to compensate expansion of the liquid in ,said channel at ambient temperatures, and means for signalling distention of said end-connected bellows at overheat temperatures.

9. Means for fire and overheat detection comprising a form-maintaining channel providing a detector volume; a bellows in communication with a zone of said channel to provide a variable compensator volume; a bellows in non-communicating parallel-acting relation with such compensa or volume and providing a volume for con- 8 trolling the same, all said volumes being liquid filled, and said control volume being distensible to provide that volumetric compensation as appropriate to compensate for ambient temperature expansion of the detector volume, and means for signalling only liquid-Vapor change expansion in the detector volume.

10. A fire and overheat detector according to claim 9 wherein the liquid filling said detector and compensator volumes is selected to boil at a predetermined overheat temperature and the liquid filling said control volume is selected and conditioned for a higher boiling point.

11. A fire and overheat detector according to claim 9 wherein said parallel acting bellows are concentric and with common walls at their ends, and the expansion in said compensator volumes anticipates that in said control volume.

12. A fire and overheat detector according to claim 9, wherein said parallel acting bellows are related by an adjustable linkage.

13. For overheat temperature alarm and control, a sensing element including a channel and coupled bellows defining a variable volume, means including an element in thermal association with said channel and definining a variable volume different from and distensible with said sensing element volume, liquids of different expansion coefiicients and boiling points filling said volumes and selected and conditioned for compensated expansion at ambient temperatures as appropriate to leave the variable volumesubstantially constant thereunder, and means for detecting at said bellows the differential distention of said volumes at temperatures above the boiling point of the lower boiling liquid.

14. Apparatus of indeterminate linearly continuous extent for overheat and fire detection and for temperature control, comprising a pressure-tight elastic chamber, an enclosed channel defining a continuously extensive temperature-sensing element, said channel in closed communication with said chamber, said channel and chamber being filled with a quantity of-liquid under conditioned predetermined boiling point, a circuit and contacts operatively related to the chamber, and volumetric compensator means associated with said sensing element whereby heating of some or all of the length of the channel thereof to a degree to or above the conditioned boiling point such as to change liquid of said length to the vapor phase thereby efiects characteristically significant operation of the contacts and heating below such degree whether due to ambient temperature change or otherwise does not efiect said characteristically significant contact operation.

References Cited in the file of this patent UNITED STATES PATENTS 1,233,746 Bendixen July 17, 1917 2,095,087 Siddall Oct. 5, 1937 2,187,061 Smith Jan. 16, 1940 2,522,248 Bair Sept. 12, 1950 2,658,190 Poitras Nov. 3, 1953 OTHER REFERENCES Aviation Week, May 1, 1950, page 25 relied on. 

